1. Field of the Invention
The invention relates to balloon catheters in which an inflation medium is used to inflate a balloon at a distal end of the catheter.
2. Description of Related Art
Catheters are known in the art and have wide medical applications. Among these applications is the infusion of fluids, medicaments and other material into the body of the patient, or the application of mechanical force such as through dilatation in constricted vessels during angioplasty. The latter procedure is best performed using balloon catheters, wherein a balloon formed on the distal end of the catheter is inflated when the catheter reaches the targeted constriction to thereby apply the requisite mechanical force to case vessel dilation.
Catheters are typically directed to the target site using guidewires, which are generally, smaller and more maneuverable. Once the guide wire is moved to the target location, the catheter is then fed over it to the target location, and therapy commences.
Balloon catheters have been constructed to have dedicated lumens for infusion, guidewire support and supply of inflation fluid to the balloon. In this manner the complexity and size of the device can be reduced, providing critical advantages when small and tortuous vessels are to be navigated.
In accordance with the invention, a catheter is provided with a lumen which serves the dual, alternate functions of supporting a guidewire or draining an inflating fluid from a balloon disposed at the distal end of the catheter. The dual functions are achieved by providing the lumen with a constricted portion forming an inflation seal which contacts a selected portion of the guidewire and forms a seal therewith when the guidewire is properly positioned in the lumen. A change in this relative positioning permits fluid flow through inflation seal and lumen, resulting in drainage of the balloon.
For optimum performance, it is contemplated that at least the inflation seal is formed of a soft material, such as Polyolefin elastomer Engage 8440 having a durometer rating material Hardness, Shore A89. The selected softness of this material enables the inflation seal to be formed with an inner diameter (ID) of the same dimension as the outer diameter (OD) of a coated section of the guidewire without significantly impeding movability of the guidewire therethrough, while at the same time maintaining a fluid-tight seal which enables the balloon to engorge with inflating fluid and thereby inflate. In designing the catheter, account may be taken of the makeup of the guidewire, which guidewire may include a hydrophilically coated coil segment. The hydrophilic coating, when hydrated during use, may undergo swelling, which will impact the interaction between the guidewire and the inflation seal in the lumen since it is contemplated that the guidewire-inflation seal interaction will occur at the hydrophilically coated coil segment of the guidewire.
The position of the inflation seal axially along the length of the catheter can be designed with a view to optimizing the flexibility or other characteristics of the catheter. To that end, the inflation seal may be placed in overlapping relationship with the balloon, or it may be placed distally from the balloon terminus, depending on the application.
Typically, catheters are provided with marker bands to enable their visualization, using medical imaging techniques, during their use in the body of the patient. In accordance with the invention, a unique scheme for attaching the marker bands to the catheter is utilized. Specifically, the marker band is integrally formed with the structure of the catheter. In this manner, the marker band will not interfere with the motion of the guidewire or increase the inner diameter of the catheter, as occurs when the marker band is affixed to the inside of the catheter as in some prior art; nor will the marker band increase the outer diameter of the catheter, as occurs when the marker band is affixedxe2x80x94using an adhesive or a shrink materialxe2x80x94to the outside of the catheter as in some of the remaining prior art. An additional advantage is a more secure attachment since the marker band is completely surrounded by the catheter material and is integrally formed therewith.